Nanocrystalline SnSe Research Articles

Influence of temperatures on structure, thermoelectric, and mechanical properties of nanocrystalline SnSe thin films deposited by thermal evaporation

The Tin Selenide (SnSe) thermoelectric materials’ high heat-electricity inter-conversion capability makes it a potential energy resource material to tap the waste heat from different industrial processing. The present work has optimized parameters for the deposition of single-phase nanocrystalline SnSe thin films using the thermal evaporation technique. The XRD, Raman Spectroscopy, SEM, EDS, Seebeck Coefficient, Electrical Conductivity, and Thermal Conductivity data analyses were used to optimize and establish the structure-thermoelectric property relationship for nanocrystalline SnSe films. The phase analysis of the SnSe thin films deposited at various substrate heating temperatures (Ts) reveals a significant influence of Ts in the evolution of a single phase of SnSe film. The films deposited at Ts ≤ 200 °C evolved with the phases of Sn, Se, and SnSe, whereas films deposited at Ts ≥ 300 °C grew with single-phase polycrystalline SnSe. An increase in crystallite size with a shape transformation from circular to elongated grains was observed with Ts. The maximum ZT value of 0.64 with a power factor value of ~2.2 μWcm-1K-2 at 750 K measuring temperature (Ta) was obtained for the SnSe film deposited at Ts = 300 °C. The change in thermoelectric properties with Ta, including a p-type to n-type transition observed at ~600 K, was correlated with the alteration of structure and the elemental composition of the deposited films after heating at 350 °C. The heating temperature significantly influenced the hardness and elastic modulus values of the films deposited at Ts ≤ 300 °C.

High-Performance Thermoelectrics Based on Solution-Grown SnSe Nanostructures.

Two-dimensional layered tin selenide (SnSe) has attracted immense interest in thermoelectrics due to its ultralow lattice thermal conductivity and high thermoelectric performance. To date, the majority of thermoelectric studies of SnSe have been based on single crystals. However, because synthesizing SnSe single crystals is an expensive, time-consuming process that requires high temperatures and because SnSe single crystals have relatively weaker mechanical stability, they are not favorable for scaling up synthesis, commercialization, or practical applications. As a result, research on nanocrystalline SnSe that can be produced in large quantities by simple and low-temperature solution-phase synthesis is needed. In this Perspective, we discuss the progress in thermoelectric properties of SnSe with a particular emphasis on nanocrystalline SnSe, which is grown in solution. We first describe the state-of-the-art high-performance single crystal and polycrystals of SnSe and their importance and drawbacks and discuss how nanocrystalline SnSe can solve some of these challenges. We illustrate different solution-phase synthesis procedures to produce various SnSe nanostructures and discuss their thermoelectric properties. We also highlight a unique solution-phase synthesis technique to prepare CdSe-coated SnSe nanocomposites and its unprecedented thermoelectric figure of merit (ZT) of 2.2 at 786 K, as reported in this issue of ACS Nano. In general, solution synthesis showed excellent control over nanoscale grain growth, and nanocrystalline SnSe shows ultralow thermal conductivity due to strong phonon scattering by the nanoscale grain boundaries. Finally, we offer insight into the opportunities and challenges associated with nanocrystalline SnSe synthesized by the solution route and its future in thermoelectric energy conversion.

Annealing Effect on the SnSe Nanocrystalline Thin Films and the Photovoltaic Properties of the p-SnSe/n-Si Heterojunction Solar Cells

A thin film of SnSe were deposited by thermal evaporation technique on 400 ±20 nm thick glass substrates of these films were annealed at different temperatures (100,150,200 ⁰C), The effect of annealing on the characteristics of the nano crystalline SnSe thin films was investigated using XRD, UV-VIS absorption spectroscopy, Atomic Force Microscope (AFM), and Hall effect measurements. The results of X-ray displayed that all the thin films have polycrystalline and orthorhombic structure in nature, while UV-VIS study showed that the SnSe has direct band gap of nano crystalline and it is changed from 60.12 to 94.70 nm with increasing annealing temperature. Hall effect measurements showed that all the films have a positive Hall coefficient, which means that the conductivity of the films is p-type. The conductivity of SnSe films was increased with increasing annealing temperatures (except that at 200⁰C). The I-V characteristics under illumination for the "p-SnSe/n-Si” solar cell displayed an increase in conversion efficiency with increasing annealing temperature from R.T to 150⁰C, while at 200⁰C, this efficiency was decreased. The measurements of the C-V characteristics displayed that all junctions were abrupt type. It is clear from C-V measurements that the capacitance decreased with increasing reverse bias voltage which leads to an increase in the depletion width.

Electrical characterization of nanocrystalline SnSe and ZnSe thin films: effect of annealing

In this paper, experimental data on the electrical properties of as deposited and annealed nanocrystalline SnSe and ZnSe thin films are reported. The thin films of SnSe and ZnSe are deposited on glass substrate by chemical bath deposition method. The films are studied before and after thermal annealing at temperatures 473 K for 1 h. This annealing is done in vacuum of 2 × 10−3 mbar. The various electrical parameters like dark conductivity, photoconductivity, activation energy, photosensitivity and carrier life time have been measured on these films before and after annealing.

Enhanced thermoelectric properties of SnSe thin films grown by pulsed laser glancing-angle deposition

SnSe single crystals have been demonstrated to possess excellent thermoelectric properties. In this work, we demonstrate a grain size control method in growing nanocrystalline SnSe thin films through a glancing angle pulsed-laser deposition approach. Structural characterization reveals that the SnSe film deposited at a normal angle has a preferred orientation along a axis, while by contrast, the SnSe film deposited at an 80° glancing angle develops a nanopillar structure with the growth direction towards the incident atomic flux. The glancing angle deposition greatly reduces the grain size of the thin film due to a shadowing effect to the adatoms, resulting in significantly increased power factor for more than 100%. The maximum Seebeck coefficient and power factor are 498.5μV/K and 18.5μWcm−1K−2, respectively. The enhancement of thermoelectric property can be attributed to the potential barrier scattering at grain boundaries owing to the reduced grain size and increased grain boundaries in the film. Given this enhanced power factor, and considering the fact that the nanopillar structure should have much lower thermal conductivity than a plain film, the zT value of such made SnSe film could be significantly larger than the corresponding single crystal film, making it a good candidate for thin film-based thermoelectric device.

Effect of deposition temperature on structural, optical and electrical properties of nanocrystalline SnSe thin films

SnSe thin films have been prepared by chemical bath deposition method at different substrate temperature. The influence of deposition temperature on structural, optical and electrical properties of polycrystalline SnSe films have been investigated using X-ray diffraction, optical absorbance and conductivity measurements. The X-ray diffraction study reveals the orthorhombic structure of the SnSe films oriented along the (111) direction. The structural parameters such as lattice spacing, crystallite size, strain, number of crystallites per unit area and dislocation density have been evaluated. Optical absorbance measurement indicates the existence of direct allowed band gap in the range 1.50–1.91 eV. The dark conductivity (σ d ) and photoconductivity (σ ph ) measurement in the temperature range (278–385 K), indicates that the conduction in these materials is through an activation process having one activation energy. σd and σ ph values decrease with the decrease of crystallite size. The value of photosensitivity, carrier life time and trap depth have also been calculated.

Synthesis and characterization of low particle size nanocrystalline SnSe thin films

Tin selenide (SnSe) nanocrystalline thin films of different thickness from 15 to 70 nm were prepared by inert gas condensation technique. Argon gas flow and substrate temperature were kept constant during deposition process at 2 × 10−3 Torr and 27 °C respectively. Polycrystalline orthorhombic phase structured was deduced for the prepared SnSe ingot powder by X-ray diffraction pattern. The grazing incident in-plane X-ray diffraction (GIIXD) pattern showed nanocrystalline orthorhombic structure for deposited SnSe thin film. The TEM micrographs showed that thin films were nanocrystalline with particle size in the range from 2 to 5.7 nm. The optical band gap Eg of the thin films due to direct allowed transition have values ranging from 2.5 to 2.13 eV as the particle size increases from 2 to 5.7 nm. The photoconductivity spectra of the nanostructured SnSe thin films of different particle size showed transitions at 2.45, 2.34 and 2.21 eV for films of different particle size.

Effects of Annealing on Thermally Evaporated SnSe Thin Films

SnSe alloy in alkaline medium was synthesized at 100°C using SnCl2.2H2O and selenium as source materials. The powder X-ray diffraction patterns recorded for synthesized product confirmed the formation of nanocrystalline SnSe material. The synthesized SnSe was made as pellets and used as the source materials for the deposition of SnSe thin films on the glass substrate by thermal evaporation method at room temperature (RT) and at various substrate temperatures of 150°C, 250°C, 350°C and 450°C. The deposited films were annealed at 450°C for 30 min under the vacuum of ∼ 10−5 Torr. The effects of annealing on the structural and optical properties of the as deposited SnSe films are reported in this article. Scanning Electron Microscopy shows the modification in surface morphology of SnSe thin films due to annealing. Annealing of the films reduces the transmittance and enhances optical band gap of SnSe films.

Synthesis and characterization of tin(II) selenide nanocrystalline by electron beam irradiation method

A novel method has been developed by electron beam irradiation to prepare nanocrystalline tin(II) selenide with an orthorhombic phase. Two megaelectron volt 10mA GJ-2-II electronic accelerator is applied as radiation resource. SnCl2, Se react under 350kGy radiation dose, and the optimal experiment condition is studied. Nanocrystalline SnSe is prepared rapidly at room temperature under atmospheric pressure, without any kind of toxic reagents. The structure and morphology of prepared SnSe nanocrystalline are analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM). The results show that the as-prepared SnSe is of high quality. TEM images reveal that the product was comprised of homogeneous and spherical grains and that the average grain size is about 50nm. The optical properties of prepared SnSe nanocrystalline are characterized by using UV–vis–NTR spectroscopy and photoluminescence spectroscopy. The prepared SnSe nanoparticles show blue shift compare to the bulk material, and the band gap energy of SnSe nanocrystalline is obtained by using the extrapolation. The possible mechanism of the SnSe grain growth by electron beam method is proposed.

Nanocrystalline tin as a preparative tool: synthesis of unprotected nanoparticles of SnTe and SnSe and a new route to (PhSe)4Sn.

The reactions of nanocrystalline tin metal (Sn*) with elemental selenium and tellurium and with the diaryldichalcogenides Ph2Se2 and Ph2Te2 have been investigated. Reaction of Sn* with the soluble tellurium source Ph2Te2 led to a clean formation of nanoparticles of cubic SnTe. Dependent on the concentration of Ph2Te2, the particles sizes could be varied between 15 and 60 nm in average, whereas the reaction of Sn* with Ph2Se2 formed molecular Sn(SePh)4 in high yield. The latter molecular compound was thermolyzed at 300 degrees C, yielding nanocrystalline SnSe with a broader distribution of size. The nanoparticles of SnTe were thoroughly investigated by transmission electron microscopy (TEM) and powder X-ray diffraction. The reactions of Sn* with elemental selenium and tellurium gave single- phase but microcrystalline SnSe and SnTe.

Room temperature growth of nanocrystalline tin (II) selenide from aqueous solution

Sheet-like nanocrystalline SnSe with an orthorhombic phase has been prepared via a reaction between a selenium alkaline aqueous solution and tin (II) complex at room temperature under atmospheric pressure. The XRD pattern indicated that the selenium alkaline solution as a selenium source, made the product to crystallize well at room temperature. The XPS analysis indicated that the purity of the product was quite high. The mechanism of the formation of tin (II) selenide was discussed.

A convenient, low temperature route to nanocrystalline SnSe

Nanocrystalline SnSe semiconductor was synthesized by a novel solvothermal method. SnCl 2, Se, and Na reacted at 130°C for 5 h in an autoclave. Ethylenediamine was used as solvent. The product was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the as-prepared SnSe was of high quality. TEM images revealed that the product was comprised of homogeneous and spherical grains and that the average grain size was about 45 nm. The possible mechanism of the SnSe grain growth is proposed.